Invasive Species Management

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Help Jeffco ISM provide residents with the information they need to manage noxious weeds and to gauge how our efforts are doing.

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Need Noxious Weed Advice?

We are not able to provide site visits in 2020 but are monitoring calls and questions. See our contact information on the right-hand side of this page.

What We Do

The Jefferson County Invasive Species Management program provides education and outreach to help Jeffco residents learn to identify and manage noxious weeds, forest insect pests and agricultural vertebrate pests.  Our goal is to provide the public with information and offer solutions that they can use to manage their weed and pest problems.

We ensure the compliance with Colorado’s noxious weed, forest pest, and agricultural vertebrate pest regulations on private, county, and state lands.  We also provide technical assistance and support to county departments who are responsible for managing county owned lands.

The program coordinates with private, local, state, and federal agencies to achieve regional pest control.

Who We Are

Our staff includes the Invasive Species Management Coordinator and limited summer help.


Bee of the Month

Each month we will feature a bee profile.  There are 100’s of species of native bees in Jeffco.  Bees support many ecological processes but often go unnoticed.  

Hunt's Bumble Bee

Bombus huntii

By Liam Cullinane, ISM Specialist

Photo Credit: bugguide

Hunt’s bumble bee (Bombus huntii)  is one of the most common bumble bee species in Colorado. Like many other bumble bee species, it is a generalist, collecting pollen and nectar from a variety of plant families, genera, and species. 

This bumble bee species nests in the ground, in already existing holes (e.g. abandoned rodent burrows, bird nests). 

Bumble bee species are somewhat unique in the bee world in that they are some of the only bee species that are highly social. A single colony of the Hunt’s bumble bee can have around 1000-2000 members throughout the growing season. In the beginning of the summer (March-May), Hunt’s bumble bee queens will emerge from their overwintering nests and begin searching for a new nest to start their colony. 

Once a nest is established, the queen will begin producing unfertilized female worker bees, which are significantly smaller in size than the queen. These workers carry out most of the pollen and nectar collection for the remainder of the season. Colony sizes reach their maximum around mid-summer (June). Then, near the end of the summer, the queen begins producing larger females (presumed to be next year’s queens), as well as male bees. 

At the end of the growing season, the queen, all worker bees, and the males perish, with only next year's queens surviving the winter. 

Make sure to look out for this species in parks and open space areas and in your garden!

Canada thistle

Weed of the Month

Each month we will feature a noxious weed to help landowners identify weeds they may encounter on their property.

Canada thistle

Cirsium arvense

Canada thistle is a perennial plant that is part of the Asteraceae family. These plants can grow anywhere from 2 to 5 feet tall. Canada thistle reproduces by seed and root propagation which results in the colony formation of this plant. Roots can grow 15 feet or more horizontally and 6 to15 feet vertically.

Leaves are 4 to 8 inches long and dark green with spiny, serrated edges. Canada thistle flowers from June to August with purple, pink or white flowers.

Canada thistle can be found in fields, riparian areas, pastures, roadsides, and lawns and gardens. Due to growing behaviors and root systems this noxious weed is one of the most widespread noxious weeds in Colorado.

Canada thistle is a List B noxious weed and in Jeffco it is slated for suppression.  Canada thistle is best controlled with mowing monthly June through September and then treating with herbicide in the fall. Canada thistle rust is a new biological control method that is showing good success in parts of Colorado.  It is available from CDA's Palisade Insectary


  1. Identify nearby populations that may spread to your property
  2. Limit disturbances on your property that can allow Canada thistle to encroach
  3. Educate your neighbors on Canada thistle so they also understand why it is important to control this noxious weed

What You Can Do

  1. Treat your Canada thistle populations and offer to help your neighbors treat theirs
  2. Report any populations you locate to your county weed coordinator
  3. Clean your gear before and after hikes to limit spread

A Landowner's Guide

Developing a Noxious Weed Management Plan

LG_NoxWeed_2020_cover Opens in new window

Download your copy

Weed Spotter

The 2020 Weed Spotter program is a citizen science based effort to detect 6 high priority species on Jeffco Open Space parks.  Learn more at our Citizen Science page.


Colorado’s Noxious Weed Awareness Campaign

2020 marks the 30th anniversary of the Noxious Weed Law. Jeffco Invasive Species Management is a partner in Colorado’s Noxious Weed Awareness Campaign.



Jefferson County Open Space will be applying herbicides for noxious weed control at the following parks.

Please give our crews and contractors room to work.  

Dates and locations subject to change.  Always visit the main kiosk at the individual park for current information.

Herbicide Treatments

Weed of 10/26/2020

  • No treatments scheduled

Week of 10/19/2020

  • Crown Hill Park
  • Lair o the Bear Park
  • North Table Mountain
  • Welchester Park,
  • White Ranch Park